Database Setup for Production 

Purpose

If you have not already set up your Informix database for live production, you can optimize your installation so that future problems can be avoided. You need to decide on the size of your dbspaces and their distribution.

Prerequisites

Be sure to talk to your hardware partner and SAP about your plans for the database. They should have used the SAP Configuration Tool to estimate how much disk space your system needs and in which dbspaces. In general, it is better to have many small disk drives than a few large ones, because this helps spread the load, so reducing potential I/O bottlenecks and improving performance.

You can also use the SAP GoingLive service for help with your implementation. For more information, see SAP Safeguarding.

Process Flow

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       1.      If you have no information on the projected size of your database, you refer to your installation notes for minimum sizes for dbspaces before productive start. If you have spare disk capacity, you can either:

¡        Wait and see how your system grows. When you have a better picture of the way individual dbspaces are growing, you can decide which dbspaces can best use the spare disk space. This is the safest option.

¡        Assign spare disk space to the dbspaces that tend on average to grow rapidly in SAP Systems, that is, PSAPCLU, PSAPBTAB, PSAPSTAB, PSAPPOOL, PSAPPROT.

Your system might not conform to the average profile. Therefore, routinely monitor all dbspaces, before deciding which ones to allocate spare disk space to.

       2.      When working out your disk layout, you aim to:

¡        Limit disk-head movement

¡        Reduce disk contention

¡        Balance the I/O load across available disks

       3.      You follow these guidelines when installing your dbspaces on the disk drives:

¡        Mirror the critical dbspaces ( ROOTDBS, PHYSDBS, and LOGDBS) as database operation crucially depends on them (this is also stressed in the installation notes). Consider mirroring other important dbspaces too.

Mirroring means that the mirror chunk of each dbspace must be on a separate physical disk drive from the corresponding primary chunk (this in any case brings a performance improvement in read operations since the most available disk is used for the read). Use disks of the same speed, otherwise the speed of the slower disk dictates the overall performance.

You can also mirror dbspaces using RAID 1. With Microsoft NT, we recommend using Informix mirroring rather than NT mirroring, because performance is better.

¡        Place the critical dbspaces – that is, ROOTDBS, PHYSDBS, and LOGDBS – on fast disk drives as they are very heavily accessed. If possible, use separate physical disks.

¡        Place the high-load dbspaces PSAPBTAB, PSAPCLU, and PSAPSTAB on separate disks to reduce disk I/O contention and use faster disk drives if available.

¡        Place the low-load dbspaces – PSAPSOURCE, PSAPDDIC, PSAPDOCU, PSAPESxxx, PSAPELxxx, and, to a certain extent, PSAPLOAD – on slower disk drives and distribute them evenly to avoid a “cold” disk (that is, one with few accesses).

¡        Place the critical dbspaces ( ROOTDBS, PHYSDBS, and LOGDBS) near the center of the disk to reduce disk-head movement. Use the same approach with the high-load SAP dbspaces ( PSAPBTAB, PSAPCLU, and PSAPSTAB).

¡        Place the low-load SAP dbspaces ( PSAPSOURCE, PSAPDDIC, PSAPDOCU, PSAPESxxx, PSAPELxxx and, to a certain extent, PSAPLOAD) towards the edge of your disks.

Result

Monitor the dbspaces in your system closely after you go live. Refer to Database Growth Monitoring.